A cap-type container of the kind with which the invention is concerned, generally has a body, a bottom rigidly and sealingly connected to the body and a top or cover likewise rigidly and sealingly connected to the body, e.g. by a folded seam at the upper chime of the body
The cover has at least one filling opening, which may hereinafter be referred to as a bunghole, surrounded by a tubular fitting over which a cap can be applied. The cap can have an internal screwthread which mates with an external screwthread on the fitting to provide a liquid tight and gas tight closure for the drum, cask or barrel.
A cap-type container of the kind described, composed of relatively thin sheet metal, can be used as a barrel or drum for a variety of liquids or flowable bulk solids. It can be used as a cask for beverages, e.g. as a beer barrel or keg.
Generally the wall thickness of the structure forming the bunghole must be relatively large in conventional barrels so that a threaded fitting adapted to form or surround the bunghole is attached to the cover of the drum or barrel by a screw connection, by rolling over sheet metal portions, by a pressing operation or by welding the fitting in or onto the cover.
As a consequence, fabrication of the container requires a larger number of parts than may be desirable to form a cover which is satisfactory and also mandates a number of fabrication steps to ensure a firm attachment of the fitting and a sealing between the fitting and the cover which can increase the cost of fabrication of the barrel to an excessive degree. Special means may be required for providing a seal between the bung and the cover and such means can include additional sealing rings.
The conventional constructions are, however, fraught with a number of problems. For example, drop tests have shown that the region between a rigid fixture or fitting and the thin sheet metal cover is subjected to local stresses which can destroy the connection or so damage it that leakage can occur.
The provision of sealing rings between the fitting and the cover not only means that additional elements are required but that a variety of considerations in the handling of the container will arise. For example, many conventional types of elastic sealing rings may not be resistant to the substances with which the container is to be filled so that the use of such sealing rings must take into consideration the ultimate use of the container and the products which are to be packaged or transported therein.
Furthermore, the use of elastic sealing rings may impede the handling of the containers since the seals may be affected by solvents and cleaning agents used in cleaning the container or by high temperatures utilized in the cleaning process.
Indeed, if the container is equipped with an elastic ring between the fitting and the cover, a variety of cleaning agents may be excluded from use and it may not be possible to employ elevated cleaning temperatures.